Negative electrode material and secondary battery

Abstract

The application relates to the technical field of battery negative electrode materials. The application discloses a negative electrode material and a secondary battery, the negative electrode material comprising a porous material and an active substance, the active substance being at least partially distributed in the pores of the porous material, and the active substance comprising a silicon material; XPS etching is performed on multiple depths from the particle surface of the negative electrode material to the particle core to obtain the Si atomic content of the multiple depths, and the Si atomic content of the particle surface and the Si atomic content of the multiple depths satisfy: gamma<=0.4. The negative electrode material according to the application has good comprehensive performance.

Description

Technical Field

[0001] This application generally relates to the field of battery anode material technology. More specifically, this application relates to an anode material and a secondary battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long lifespan, and no environmental pollution, are widely used in the 3C field (communication, computer, and consumer electronics) and large equipment such as electric vehicles and power tools. To improve battery energy density, silicon-based anode materials, due to their low voltage platform, environmental friendliness, and abundant resources, have become one of the most promising materials for achieving high-capacity lithium-ion batteries. However, existing ordinary silicon-based materials have many problems. During charge and discharge, their large volume expansion easily leads to particle pulverization and detachment from the current collector. Simultaneously, the repeated volume changes of silicon-based active materials during electrochemical cycling cause the surface-formed SEI film ("Solid Electrolyte Interphase") to continuously break down and regenerate, continuously consuming lithium ions, severely affecting battery stability, and leading to a rapid decline in battery capacity during long cycles.

[0003] Therefore, there is an urgent need to provide a solution for anode materials in order to improve the cycle stability of anode materials. Summary of the Invention

[0004] In order to at least solve one or more of the technical problems mentioned above, this application proposes a solution for a negative electrode material and a secondary battery in several aspects.

[0005] In a first aspect, this application provides a negative electrode material comprising a porous material and an active material, wherein the active material is at least partially distributed within the pores of the porous material, and the active material comprises silicon. XPS etching is performed from the particle surface of the negative electrode material to multiple depths towards the particle core to obtain the Si atom content at the multiple depths, wherein the Si atom content at the particle surface and the Si atom content at the multiple depths satisfy the following: ; γ≤0.4; where γ represents the uniformity parameter of Si atom distribution in the negative electrode material, A i A represents the Si atom content at the i-th depth out of n depths from the particle surface to the particle core of the negative electrode material. i-1 A0 represents the Si atom content at the (i-1)th depth out of n depths from the particle surface to the particle core of the negative electrode material, D represents the distance between the i-th depth and the (i-1)th depth, and n≥2.

[0006] In some embodiments, the Si atom content at each depth from the particle surface to the particle core of the negative electrode material is 17% to 25%.

[0007] In other embodiments, the Si atom content on the particle surface is 5% to 17%; and the Si atom content at each depth from the particle surface to the particle core of the negative electrode material is 5% to 17%.

[0008] In some other embodiments, the average Si atom content from the particle surface of the negative electrode material to the third depth is less than the average Si atom content from the fourth depth to the eighth depth.

[0009] In some embodiments, the negative electrode material further satisfies at least one of the following characteristics: (1) the volume ratio of micropores to total pore volume in the negative electrode material is ≤10%; (2) the volume ratio of mesopores to total pore volume in the negative electrode material is ≥80%; (3) the volume ratio of macropores to total pore volume in the negative electrode material is ≤20%; (4) the total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.1cm 3 / g; (5) the average pore size of the negative electrode material is 0.45nm~50nm; (6) the specific surface area of ​​the negative electrode material is 0.5m². 2 / g~10m 2 / g.

[0010] In other embodiments, after the silicon material is removed, the negative electrode material satisfies at least one of the following characteristics: (1) the total pore volume is 0.2 cm³. 3 / g~1.5cm 3 / g; (2) Micropores account for ≥15% of the total volume of all pores; (3) Mesopores account for ≤85% of the total volume of all pores; (4) Macropores account for ≤2% of the total volume of all pores; (5) Pores smaller than 5nm account for ≥90% of the total volume of all pores; (6) Specific surface area is 200m² 2 / g~3000m 2 / g; (7) Average pore size is 1.0nm~20nm; (8) True density is 1.6g / cm³ 3 ~2.4g / cm 3 .

[0011] In some other embodiments, the negative electrode material also satisfies at least one of the following characteristics: (1) the particle size distribution of the negative electrode material satisfies: 0.9≤(Dv90-Dv10) / Dv50≤5; (2) the volume median particle size Dv50 of the negative electrode material is 0.5μm~40μm; (3) the volume median particle size Dv50 of the negative electrode material is 5μm~20μm.

[0012] In some embodiments, the negative electrode material also satisfies at least one of the following characteristics: (1) the compaction density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 (2) The tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5g / cm 3 (3) The powder conductivity of the negative electrode material under 20kN pressure is 0.1S / cm~2S / cm; (4) The gas production of the negative electrode material is ≤1mL / g / day.

[0013] In other embodiments, the negative electrode material also satisfies at least one of the following characteristics: (1) the porous material includes at least one of activated carbon, capacitor carbon, carbon molecular sieve, graphene, zeolite, porous graphite, porous Al2O3, porous ZrO2, and porous TiO2; (2) the negative electrode material further includes a core and a carbon coating layer covering at least a portion of the surface of the core, the core comprising a porous material and an active substance; (3) based on the mass of the negative electrode material, the mass content of silicon in the negative electrode material is 20% to 60%; (4) based on the mass of the negative electrode material, the mass content of carbon in the negative electrode material is 35% to 80%.

[0014] In a second aspect, this application provides a secondary battery comprising the negative electrode material described in any one of the first aspects of this application.

[0015] In the above-mentioned anode material scheme, the anode material of this application embodiment includes a porous material and an active material. XPS etching is performed from the particle surface of the anode material to multiple depths from the particle core to obtain Si atom content at multiple depths. The Si atom content at the particle surface and the Si atom content at multiple depths satisfy the following: Furthermore, γ≤0.4 indicates that the Si atom content of the negative electrode material particles is uniformly distributed from the surface to the interior, which is beneficial to the stress distribution inside the negative electrode material particles. This enables the negative electrode material to maintain good cycle stability in the battery, thereby obtaining excellent cycle performance and exhibiting excellent first discharge specific capacity and first coulombic efficiency. Attached Figure Description

[0016] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein:

[0017] Figure 1 A schematic diagram of a battery in a discharged state, i.e., during operation, is shown.

[0018] Figure 2 An exemplary flowchart of a method for preparing a negative electrode material according to some embodiments of this application is shown. Detailed Implementation

[0019] The technical solutions of the embodiments of this application 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 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.

[0020] 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.

[0021] 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.

[0022] 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]."

[0023] 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.

[0024] Figure 1 This diagram shows a battery in a discharged state, i.e., during operation. Figure 1 As shown, the electrode assembly includes a positive electrode 110, a negative electrode 120, and a separator 130, with the separator 130 disposed between the positive electrode 110 and the negative electrode 120. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 110, the separator 130, and the negative electrode 120. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0025] Positive electrode tablets:

[0026] The positive electrode 110 includes a positive current collector 111 and a positive active layer 112 disposed on at least one surface of the positive current collector. The positive current collector 111 can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining a conductive foil and a polymer substrate. The positive active layer 112 contains a positive active material, which includes compounds that reversibly insert and extract 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 the following: O4 or lithium iron phosphate (LiFePO4).

[0027] Negative electrode plate:

[0028] The negative electrode 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector 121. The negative electrode current collector 121 can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collectors, 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 122 includes a negative electrode material.

[0029] During battery operation, i.e. when the battery is in a discharge state, metal ions 140 (e.g., lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the electrolyte / electrolyte through the separator 130, 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 130, 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 inventors have discovered that the uniformity of active material (e.g., silicon) deposition within anode material particles significantly affects the performance of the anode material. If the Si content distribution within the anode material particles is uneven from the inside out, the stress in different parts of the particles will become uneven during repeated charge-discharge cycles. This stress imbalance leads to stress concentration at certain points with higher local stress, increasing the probability of particle breakage or pulverization at those points, resulting in deterioration of the anode material's cycle performance. Therefore, the smaller the variation in Si content distribution within the anode material particles from the inside out, the better it is for maintaining the cycle stability of the anode material, resulting in good cycle performance.

[0033] Based on the above findings, this application aims to provide a negative electrode material with a uniform Si atom content distribution, in order to improve the cycle performance of the negative electrode material. A detailed description follows.

[0034] In a first aspect, this application provides a negative electrode material comprising a porous material and an active material, wherein the active material is at least partially distributed within the pores of the porous material, and the active material comprises silicon material; XPS etching is performed from the particle surface of the negative electrode material to multiple depths towards the particle core to obtain Si atom content at multiple depths, wherein the Si atom content at the particle surface and the Si atom content at the multiple depths satisfy:

[0035]

[0036] And γ≤0.4;

[0037] Where γ represents the uniformity parameter of Si atoms in the negative electrode material, and A i A represents the Si atom content at the i-th depth out of n depths from the particle surface to the particle core of the negative electrode material. i-1 A0 represents the Si atom content at the (i-1)th depth out of n depths from the particle surface to the particle core of the negative electrode material, D represents the distance between the i-th depth and the (i-1)th depth, and n≥2.

[0038] XPS etching at multiple depths from the surface of the anode material particles towards the particle core to obtain the Si atom content at multiple depths refers to using XPS etching technology to etch multiple depths from the particle surface of the anode material towards the internal core, and measuring the Si atom content at different depth locations. The Si atom content mentioned in this article refers to the percentage of Si atoms.

[0039] X-ray photoelectron spectroscopy (XPS) etching is a surface analysis technique that combines XPS and ion etching. The basic principle of XPS is to irradiate the sample surface with X-rays, exciting electrons in the sample atoms to form photoelectrons. By measuring the energy and intensity of these photoelectrons, information such as the elemental composition and chemical state of the sample surface can be obtained. Ion etching, on the other hand, uses a high-energy ion beam (such as an argon ion beam) to bombard the sample surface, removing atoms layer by layer, thus enabling analysis at different depths of the sample. By alternating between ion etching and XPS measurements, information on the elemental distribution of the sample from its surface to its interior depths can be obtained.

[0040] This application employs XPS etching technology, which characterizes a series of particles within a specific area. The overall situation is reflected by averaging the test results of multiple particles, avoiding the randomness of particle selection. Furthermore, the machine uniformly etches the particle surface, strictly adhering to a pre-set program, unaffected by human factors, ensuring the standardization and objectivity of the testing process. Therefore, this application uses XPS etching technology to etch from the particle surface of the negative electrode material to multiple depths towards the particle core, obtaining the Si atom content at these depths. By calculating the γ value using Formula 1, the uniformity of Si atom distribution within the particle can be accurately quantified.

[0041] A value of γ ≤ 0.4 indicates a relatively uniform distribution of Si atoms from the surface to the core of the anode material particles. This effectively avoids stress concentration caused by uneven Si atom distribution, thereby improving the stability of the anode material during charge and discharge. Furthermore, the anode material exhibits excellent initial discharge specific capacity and initial coulombic efficiency. For example, γ can be 0.4, 0.3, 0.25, 0.2, 0.15, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, or other values ​​not exceeding 0.4. In some preferred embodiments, γ ≤ 0.3. If γ > 0.4, it indicates a significant difference in Si atom content at different depths within the anode material particles. This suggests a relatively uneven distribution of Si atoms within the particles, potentially leading to stress imbalance and affecting the overall performance of the anode material, including cycle stability, initial discharge specific capacity, and initial coulombic efficiency.

[0042] In other implementations, the distance between any two adjacent depths in the n depths is equal. Compared to unequal distances between any two adjacent depths in the n depths, equal distances facilitate etching operations (i.e., equidistant etching is easier to perform) and ensure that the assessment of the Si atom content distribution at different depths within the particle is uniform. This uniform assessment helps to more accurately reflect the distribution of Si elements within the particle, thus making the value of γ more representative.

[0043] In some implementations, the distance D between any two adjacent depths in the n depths can be set to 20 nm. If D is set too small, more etching steps are required to cover the same depth range, which may increase testing time and cost, and may also be limited by instrument accuracy. If D is set too large, fewer etching steps are required to cover the same depth range, which can improve testing speed, but may miss information at intermediate depths and fail to provide sufficiently fine information on Si element distribution, resulting in insufficient sensitivity to the evaluation of Si element distribution. Therefore, when D = 20 nm, it can provide a relatively fine Si atom content distribution to ensure the accuracy of the evaluation results of the uniformity of Si atom distribution in the anode material, while also helping to control testing costs.

[0044] Furthermore, in Formula 1, 'n' represents the number of depths selected when obtaining the Si atom content through XPS etching from the surface of the anode material particle to its core; that is, the number of depths used in Formula 1 for calculation. 'n' is a positive integer. For example, in some implementations, n ≥ 7. For instance, n can be 7, 8, 9, 10, 11, or 12, or other values. A larger value for 'n' allows for the acquisition of sufficient depth information, more comprehensively reflecting the elemental distribution at different locations within the particle, and is more conducive to obtaining a more accurate evaluation result of the uniformity of Si atom distribution in the anode material. However, as the value of 'n' increases, the testing time and cost also increase.

[0045] In some other embodiments, the Si atom content at each depth from the particle surface to the particle core of the negative electrode material is 17% to 25%. Exemplarily, the Si atom content at each depth can be any value among 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%, or other values ​​within the range of 17% to 25%. The Si atom content at different depths can be the same or different.

[0046] In some embodiments, the Si atom content on the particle surface is 5% to 17%, and the Si atom content at each depth from the particle surface to the particle core is 5% to 17%. Exemplarily, the Si atom content on the particle surface and at each depth can be any value from 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, or other values ​​within the range of 5% to 17%. The Si atom content on the particle surface and the Si atom content at different depths can be the same or different.

[0047] Within the aforementioned range, the Si atom content ensures that silicon, as the active material, provides high battery capacity while maintaining the stability of the anode material during cycling. It also reflects the uniformity of Si atom content at different depths within the anode material particles. If the Si atom content is too low, the battery capacity will be insufficient to meet high energy density requirements; if the Si atom content is too high, excessive volume changes in the active material during charging and discharging will damage the anode material's structure, reduce its cycle performance, and ultimately affect battery life.

[0048] In other embodiments, the average Si atom content from the particle surface to the third depth of the anode material is less than the average Si atom content from the fourth to the eighth depth. This distribution indicates that the Si atom content inside the anode material particles gradually increases from the surface to the core, forming a gradient distribution. This gradient distribution helps improve the cycle performance of the anode material. Specifically, a higher Si atom content inside the particles can provide higher capacity, while a lower Si atom content on the surface of the anode material particles can reduce stress concentration on the particle surface, which is beneficial to improving the cycle stability of the material. Furthermore, if the surface Si atom content is too high, it may lead to the formation of a dense silicon shell on the pore surface of the particles (i.e., "pore sealing"), hindering the insertion and extraction of lithium ions, while increasing the risk of SEI film formation and lithium ion consumption. A lower surface Si content can avoid this problem and maintain the open structure of the material.

[0049] Porous materials can serve as a matrix for negative electrode materials, and the desired negative electrode material can be obtained by depositing active substances in the porous material. In some embodiments, the porous material includes at least one of activated carbon, capacitor carbon, carbon molecular sieve, graphene, zeolite, porous graphite, porous Al2O3, porous ZrO2, porous TiO2, etc.

[0050] The active substance is at least partially distributed within the pores of the porous material; it may be a portion of the active substance distributed within the pores of the porous material, or it may be all of the active substance distributed within the pores of the porous material.

[0051] In other embodiments, the silicon material may include at least one of elemental silicon, silicon oxide, and silicon alloy.

[0052] When the silicon material includes elemental silicon, the elemental silicon includes one or more of amorphous silicon, crystalline silicon, and composites of crystalline and amorphous silicon. Preferably, the elemental silicon includes amorphous silicon, which expands isotropically during lithium intercalation, reducing the collapse of pores in the matrix, suppressing the rapid decay of the specific capacity of the battery including the negative electrode material, and further improving the lithium intercalation cycle performance of the negative electrode material.

[0053] When silicon materials include silicon oxides, the general formula for silicon oxides is SiOx, where 0 < x ≤ 2. Silicon oxide is a silicon-oxygen complex containing oxygen atoms and silicon atoms, with a molar ratio of oxygen atoms to silicon atoms of 0 to 2, excluding 0. It can be Si, SiO... 0.2 SiO 0.5 SiO 0.8 SiO, SiO 1.2 SiO 1.5 SiO 1.8 It can be a substance composed of two or more of the above-mentioned materials, such as SiO2, or other values ​​within the above range. This application does not impose any restrictions on these values.

[0054] When silicon materials include silicon alloys, the silicon alloys can be silicon-lithium alloys, silicon-magnesium alloys, etc. Of course, it should be noted that in some cases, silicon alloys include elemental silicon particles and alloys.

[0055] In some embodiments, the silicon material further includes silicon particles and a silicon oxide layer on the surface of the silicon particles. The silicon oxide layer includes silicon oxide with the general formula SiOx, where 0.5 ≤ x < 2. Specifically, SiOx may specifically be SiO 0.5 SiO 0.7 SiO 0.9 SiO, SiO 1.2 SiO 1.5 SiO 1.8 SiO 1.9 etc. are not specified here.

[0056] In some embodiments, the silicon material further includes silicon particles and a silicon oxide layer on the surface of the silicon particles. Based on the mass of the silicon material, the mass percentage of oxygen atoms in the silicon material is between 1% and 18%. Specifically, the mass percentage of oxygen atoms in the silicon material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or any value within the range of any two of the above values. Controlling the mass percentage of oxygen atoms in the silicon material within the above range is beneficial for forming a stable silicon oxide layer on the surface of the silicon particles, reducing direct contact between the silicon particles and the electrolyte, thereby reducing side reactions between the silicon particles and the electrolyte, and improving the cycle stability of the negative electrode material; it can also maintain the stable activity of the silicon-based material and increase the specific capacity of the negative electrode material.

[0057] In some embodiments, the particle size distribution of the negative electrode material satisfies: 0.9 ≤ (Dv90 - Dv10) / Dv50 ≤ 5. Dv10 represents the particle size corresponding to a cumulative particle size distribution volume percentage of 10%. Dv90 represents the particle size corresponding to a cumulative particle size distribution volume percentage of 90%. Dv50 represents the particle size corresponding to a cumulative particle size distribution volume percentage of 50%. Exemplarily, (Dv90 - Dv10) / Dv50 of the negative electrode material can be 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, etc., or other values ​​within the range of 0.9 to 5.

[0058] In other embodiments, the volumetric median particle size Dv50 of the negative electrode material is 0.5 μm to 40 μm. Exemplarily, the Dv50 of the negative electrode material is 0.5 μm, 1 μm, 2 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 35 μm, 36 μm, 38 μm, 40 μm, etc., or other values ​​within the range of 0.5 μm to 40 μm. In some preferred embodiments, the volumetric median particle size Dv50 of the negative electrode material is 5 μm to 20 μm.

[0059] The particle size distribution of the negative electrode material satisfies the condition: 0.9 ≤ (Dv90 - Dv10) / Dv50 ≤ 5, indicating that the particle size distribution of the negative electrode material is relatively uniform. This uniform particle size distribution helps to improve the electrochemical performance of the negative electrode material because materials with uniform particle size have a more uniform stress distribution during charge and discharge, thereby reducing the risk of particle breakage and improving the cycle stability of the battery.

[0060] If (Dv90-Dv10) / Dv50 is too small, it indicates that there are many small particles in the negative electrode material, which may lead to an excessively large specific surface area, increasing side reactions and negatively impacting the electrochemical performance of the negative electrode material. If (Dv90-Dv10) / Dv50 is too large, it indicates that there are many large particles in the negative electrode material, which may affect the conductivity of the negative electrode material and increase its secondary expansion rate.

[0061] In some embodiments, the compaction density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 For example, the compaction density of the negative electrode material can be 0.8 g / cm³. 3 0.9g / cm 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 etc., or 0.8g / cm 3 ~1.3g / cm 3 Other values ​​within the range. Compacted density refers to the density of a material during the compaction process, and is commonly used to describe the compactness of battery materials. In the manufacturing process of lithium-ion batteries, compacted density has a significant impact on battery performance. The higher the compacted density, the higher the battery capacity is generally; therefore, compacted density is also considered one of the reference indicators for material energy density. Controlling the compacted density within the above-mentioned range is beneficial for improving the capacity of the negative electrode material. If the compacted density is too low, the capacity of the negative electrode material will be too low. If the compacted density is too high, it may increase the internal resistance of the battery, thereby affecting the battery's charge and discharge efficiency.

[0062] In other embodiments, the tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5g / cm 3 For example, the tap density of the negative electrode material can be 0.5 g / cm³. 3 0.6g / cm 3 0.7g / cm 3 0.8g / cm 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 etc., or 0.5g / cm 3 ~1.5g / cm 3Other values ​​within the range. Tap density refers to the mass per unit volume of powder in a container after it has been tapped under specified conditions. Tap density reflects the compactness of the material particles; a high tap density is beneficial for improving the volumetric energy density of the battery. Both excessively high and low tap densities are detrimental to the processing performance of the negative electrode material.

[0063] In some other embodiments, the powder conductivity of the negative electrode material at a pressure of 20 kN is 0.1 S / cm to 2 S / cm. Exemplarily, the powder conductivity of the negative electrode material at a pressure of 20 kN can be 0.1 S / cm, 0.2 S / cm, 0.3 S / cm, 0.4 S / cm, 0.5 S / cm, 0.6 S / cm, 0.7 S / cm, 0.8 S / cm, 0.9 S / cm, 1 S / cm, 1.1 S / cm, 1.2 S / cm, 1.3 S / cm, 1.4 S / cm, 1.5 S / cm, 1.6 S / cm, 1.7 S / cm, 1.8 S / cm, 1.9 S / cm, 2 S / cm, etc., or other values ​​within the range of 0.1 S / cm to 2 S / cm.

[0064] When the powder conductivity of the negative electrode material is within the above-mentioned range under 20 kN pressure, it indicates that the negative electrode material has good conductivity, which is beneficial to improving the battery's charge and discharge efficiency, reducing the battery's charge and discharge impedance, and also reducing the charge transport impedance during battery cycling, thereby improving the battery's cycle stability and extending its lifespan. If the powder conductivity of the negative electrode material is too low, it indicates poor conductivity, resulting in high resistance, affecting the battery's charge and discharge efficiency, and leading to prolonged charge and discharge time. If the powder conductivity is too high, it may lead to excessively high electron concentration on the surface of the negative electrode material, thereby triggering more side reactions. For example, it may accelerate the decomposition of the electrolyte or the formation of the SEI film. These side reactions consume lithium ions, reducing the battery's coulombic efficiency and cycle life.

[0065] In some implementations, the gas production rate of the negative electrode material is ≤1 mL / g / day. A lower gas production rate indicates better chemical stability of the negative electrode material in the battery system, reducing problems such as battery bulging and short circuits caused by gas production, thereby improving battery safety and lifespan. If the gas production rate is too high, it will increase the internal pressure of the battery, posing a safety hazard, and will also affect the battery's electrochemical performance.

[0066] In other embodiments, the total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.1cm 3 / g. For example, the total pore volume of the negative electrode material can be 0.001 cm³. 3 / g, 0.005cm 3 / g, 0.01cm3 / g, 0.015cm 3 / g, 0.02cm 3 / g, 0.025cm 3 / g, 0.03cm 3 / g, 0.035cm 3 / g, 0.04cm 3 / g, 0.045cm 3 / g, 0.05cm 3 / g, 0.055cm 3 / g, 0.06cm 3 / g, 0.065cm 3 / g, 0.07cm 3 / g, 0.075cm 3 / g, 0.08cm 3 / g, 0.085cm 3 / g, 0.09cm 3 / g, 0.095cm 3 / g, 0.1cm 3 / g, or 0.001cm 3 / g~0.1cm 3 Other values ​​within the range of / g. The total pore volume of the negative electrode material refers to the pore volume of all the pores in the negative electrode material. A suitable total pore volume helps to mitigate the volume changes of silicon materials during charging and discharging. If the total pore volume is too large, it will result in lower particle strength of the negative electrode material, making it prone to breakage during the pressing of the negative electrode material into an electrode sheet.

[0067] Generally speaking, pores with a diameter ≤ 2 nanometers (nm) are called micropores, pores with a diameter between 2 nanometers and 50 nanometers (nm) are called mesopores, and pores larger than 50 nanometers are called macropores. The total pore volume of a negative electrode material includes the sum of the micropore volume, mesopore volume, and macropore volume.

[0068] In other embodiments, the volume ratio of the micropore volume of the negative electrode material to the total pore volume is ≤10%. For example, the volume ratio of the micropore volume of the negative electrode material to the total pore volume can be 10%, 9.5%, 9%, 8.5%, 8%, 7.5%, 7%, 6.5%, 6%, 5.5%, 5%, or other values ​​≤10%.

[0069] In some embodiments, the mesopore volume of the negative electrode material accounts for ≥80% of the total pore volume. Exemplarily, the mesopore volume of the negative electrode material can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or other values ​​≥80%. This shows that mesopores are the predominant pore type among all the pores in the negative electrode material. A high proportion of mesopores is beneficial for electrolyte penetration and ion transport, thus improving the charge and discharge efficiency of the battery.

[0070] In some embodiments, the volume ratio of macropores in the negative electrode material to the total pore volume is ≤20%. Exemplarily, the volume ratio of macropores in the negative electrode material to the total pore volume can be 20%, 19.5%, 19%, 18.5%, 18%, 17.5%, 17%, 16.5%, 16%, 15.5%, 15%, 14.5%, 14%, 13.5%, 13%, 12.5%, 12%, 11.5%, 11%, 10.5%, 10%, 9%, 7%, 5%, 3%, 1%, or other values ​​≤20%.

[0071] In some embodiments, the average pore size of the negative electrode material is 0.45 nm to 50 nm. Exemplarily, the average pore size of the negative electrode material can be 0.45 nm, 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or other values ​​within the range of 0.45 nm to 50 nm. An appropriate average pore size facilitates sufficient contact between the electrolyte and the negative electrode material, thereby improving the lithium-ion insertion / extraction kinetics and enhancing the rate performance of the battery. An excessively small average pore size may result in insufficient contact area between the electrolyte and the negative electrode material, affecting lithium-ion transport efficiency. An excessively large average pore size may result in an excessively large contact area between the electrolyte and the negative electrode material, increasing the likelihood of side reactions.

[0072] In some implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~10m 2 / g. For example, the specific surface area of ​​the negative electrode material can be 0.5m². 2 / g, 1.0m 2 / g, 2.0m 2 / g, 3.0m 2 / g, 4.0m 2 / g, 5.0m 2 / g, 6.0m 2 / g, 7.0m 2 / g, 8.0m 2 / g, 9.0m 2 / g, 10m 2 / g, or 0.5m 2 / g~10m 2 Other values ​​within the / g range.

[0073] An appropriate specific surface area can balance the reactivity and irreversible capacity of a material. The specific surface area of ​​the negative electrode material affects the contact area between the negative electrode material and the electrolyte. A specific surface area within the aforementioned range allows for a suitable contact area between the negative electrode material and the electrolyte, thereby enhancing reactivity and improving rate performance while controlling irreversible capacity within an acceptable range. An excessively small specific surface area means insufficient contact area between the negative electrode material and the electrolyte, potentially leading to reduced lithium-ion transport efficiency, low reactivity, and poor rate performance. An excessively large specific surface area will result in a significant increase in irreversible capacity, affecting the efficiency of the battery during the first charge and discharge process (first coulombic efficiency, or "first efficiency"), thus reducing the first efficiency.

[0074] In other embodiments, the total pore volume of the anode material after removing the silicon material is 0.2 cm³. 3 / g~1.5cm 3 / g. In some embodiments, the negative electrode material, after removing the silicon material, becomes a porous material. For example, the total pore volume of the negative electrode material after removing the silicon material can be 0.2 cm³. 3 / g, 0.3cm 3 / g, 0.4cm 3 / g, 0.5cm 3 / g, 0.6cm 3 / g, 0.7cm 3 / g, 0.8cm 3 / g, 0.9cm 3 / g, 1.0cm 3 / g, 1.1cm 3 / g, 1.2cm 3 / g, 1.3cm 3 / g, 1.4cm 3 / g, 1.5cm 3 / g, or 0.2cm 3 / g~1.5cm 3 Other values ​​within the / g range.

[0075] In some other embodiments, the volume percentage of micropores in the anode material without silicon is ≥15% of the total volume of all pores. For example, the volume percentage of micropores in the anode material without silicon can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or other values ​​≥15%. It can be seen that the volume percentage of micropores in the anode material without silicon is greater than the volume percentage of micropores in the anode material itself. When the volume of micropores in the anode material without silicon is large, the capillary effect of the micropores makes it easier for the active silicon material to preferentially deposit into the micropores, which is beneficial for controlling the growth of the active material into nanoscale silicon and for increasing the deposition amount of the active material.

[0076] In some implementations, the volume fraction of mesopores in the anode material, which removes silicon material, is ≤85% of the total volume fraction of all pores. Exemplarily, the volume fraction of mesopores in all pores can be 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, or other values ​​≤85%.

[0077] In other embodiments, the volume percentage of macropores in the silicon-removed anode material is ≤2% of the total volume of all pores. Exemplarily, the volume percentage of macropores in all pores can be 2%, 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, or other values ​​≤2%. Therefore, a smaller volume percentage of macropores in the silicon-removed anode material effectively avoids the problem of active material mainly depositing in macropores, potentially forming large-grained active material, which would hinder the control of active material expansion during battery charging and discharging.

[0078] In some other embodiments, the volume percentage of pores smaller than 5 nm in the silicon-removed anode material is ≥90% of all pores. For example, the volume percentage of pores smaller than 5 nm in all pores can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or other values ​​≥90%. In this embodiment, the presence of pores smaller than 5 nm as the majority of all pores in the silicon-removed anode material not only improves the deposition amount of active material but also helps control the growth of active material, thereby controlling the expansion volume of active material during battery charging and discharging.

[0079] In some embodiments, the specific surface area of ​​the anode material without silicon is 200 m². 2 / g~3000m2 / g. For example, the specific surface area of ​​the anode material with silicon removed can be 200m². 2 / g、400m 2 / g、500m 2 / g、600m 2 / g、800m 2 / g, 1000m 2 / g、1200m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g、1800m 2 / g、2000m 2 / g、2200m 2 / g、2400m 2 / g、2500m 2 / g、2600m 2 / g、2800m 2 / g、3000m 2 / g, or 200m 2 / g~3000m 2 Other values ​​within the / g range.

[0080] The removal of silicon from the anode material, i.e., porous materials, provides more active sites for subsequent silicon deposition due to their larger specific surface area. During silicon deposition, silicon atoms can be more uniformly dispersed within the pores of the porous material, forming a more stable structure. This helps improve the overall performance of the anode material; for example, during charge and discharge, uniformly dispersed silicon can participate more effectively in electrochemical reactions, reducing structural damage caused by localized stress concentration and improving battery cycle stability. Too small a specific surface area cannot provide sufficient sites for the growth of nano-silicon. Too large a specific surface area weakens the structural stability of the anode material, thus affecting subsequent processing performance.

[0081] In some embodiments, the average pore size of the anode material without silicon is 1.0 nm to 20 nm. Exemplarily, its average pore size can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, etc., or other values ​​within the range of 1.0 nm to 20 nm.

[0082] In other embodiments, the true density of the anode material without silicon is 1.6 g / cm³. 3 ~2.4g / cm 3For example, the true density of the anode material without silicon can be 1.6 g / cm³. 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 2.0g / cm 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 Wait, or 1.6 g / cm 3 ~2.4g / cm 3 Other values ​​within the range.

[0083] In other embodiments, the negative electrode material includes a core and a carbon coating layer covering at least a portion of the surface of the core, the core comprising a porous material and an active substance. In some embodiments, the carbon coating layer covering at least a portion of the surface of the core may include a carbon coating layer covering a portion of the surface of the core, or it may include a carbon coating layer covering the entire surface of the core.

[0084] In some embodiments, the carbon coating layer may include carbon materials, which may include one or more of graphene, soft carbon, and hard carbon. The carbon coating layer possesses good electrical conductivity, which can improve the conductivity of the negative electrode material. Furthermore, the carbon coating layer located on the surface of the negative electrode material can protect the porous material on which the active material is deposited, reducing direct contact between the active material and the electrolyte, and improving the stability of the SEI film ("Solid Electrolyte Interface membrane"). This, in turn, is beneficial for further improving the cycle life and rate performance of the negative electrode material.

[0085] In some embodiments, the carbon 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. Understandably, when the carbon coating layer has a multi-layer coating structure, the density is higher.

[0086] In some embodiments, the silicon content in the negative electrode material is 20% to 60% by mass, based on the mass of the negative electrode material. Exemplarily, the silicon content in the negative electrode material can be 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, 46%, 48%, 50%, 52%, 54%, 55%, 56%, 58%, 60%, or other values ​​within the range of 20% to 60%. Within this range, the silicon content can control the volume change of the material while ensuring high battery capacity, thereby achieving stable cycle performance. If the silicon content is too low, the high capacity advantage of silicon cannot be fully utilized. If the silicon content is too high, it will cause excessive volume expansion of the negative electrode material during cycling, affecting battery stability and reversible charge-discharge performance.

[0087] In other embodiments, the carbon content in the negative electrode material is 35% to 80% by mass, based on the mass of the negative electrode material. This carbon originates from the carbon coating layer and / or porous materials. Exemplarily, the carbon content in the negative electrode material can be 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or other values ​​within the range of 35% to 80%. Within this range, the carbon content serves both to improve conductivity and mitigate the volume expansion of the negative electrode material, thereby improving its cycle performance. If the carbon content is too low, it will reduce the conductivity and structural stability of the negative electrode material. If the carbon content is too high, it will lead to a reduction in the deposition of active material, thus decreasing the battery capacity.

[0088] It is understood that the negative electrode material in the embodiments of this application may include oxygen and / or other elements in addition to the silicon and carbon elements mentioned above. This application does not impose any limitations on this.

[0089] In another aspect, this application also provides a method for preparing a negative electrode material, so as to obtain a negative electrode material with the aforementioned characteristics. The following will be combined with... Figure 2 An illustrative example is provided.

[0090] Figure 2 An exemplary flowchart illustrating a method for preparing a negative electrode material according to some embodiments of this application is shown. Figure 2As shown, the preparation method 200 may include: in step S201, loading a porous material into a vapor deposition apparatus; in step S202, introducing a silicon-containing gas into the vapor deposition apparatus in a pulsed manner to deposit silicon material in the pores of the porous material to obtain a negative electrode material; wherein the pulse pressure during the deposition process is controlled to be -3kPa to 7kPa, the frequency of the pulse bias voltage is 200Hz to 1000Hz, and the duty cycle is 0.15 to 0.85.

[0091] In some embodiments, the preparation method 200 further includes step S204, in which a carbon source gas is introduced into a vapor deposition apparatus to coat the outer surface of the negative electrode material obtained in step S202 with a carbon material to obtain the final negative electrode material.

[0092] In some embodiments, the vapor deposition apparatus may include, for example, a vapor deposition furnace. In other embodiments, the amount of porous material loaded may be 1 kg to 5 kg, such as 1 kg, 1.5 kg, 2 kg, 2.5 kg, 3 kg, 3.5 kg, 4 kg, 4.5 kg, 5 kg, or other values ​​within the range of 1 kg to 5 kg.

[0093] In other embodiments, the porous material may include at least one of activated carbon, capacitive carbon, carbon molecular sieve, graphene, zeolite, porous graphite, porous Al2O3, porous ZrO2, porous TiO2, etc. In still other embodiments, in step S201, after loading the porous material into the vapor deposition equipment, a vacuum of 10... -4 ~10Pa.

[0094] In some embodiments, before step S202, the preparation method 200 may further include step S203, whereby, under a protective gas flow, the heating system of the vapor deposition apparatus is activated to heat the vapor deposition apparatus. In other embodiments, the heating rate is 1°C / min to 10°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or other values ​​within the range of 1°C / min to 10°C / min.

[0095] In some embodiments, the protective gas in step S203 can be an inert gas. In still other embodiments, the protective gas can include one or more of nitrogen, argon, and helium. In some embodiments, the flow rate of the protective gas is 0.5 L / min to 60 L / min, for example, it can be 0.5 L / min, 1 L / min, 2 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, 55 L / min, 60 L / min, etc., or other values ​​within the range of 0.5 L / min to 60 L / min. In some preferred embodiments, the flow rate of the protective gas can be 2 L / min to 50 L / min. In a further preferred embodiment, the flow rate of the protective gas can be 5 L / min to 20 L / min.

[0096] In some implementations, the oxygen content after the protective gas is introduced into the vapor deposition equipment is less than 50 ppm, at which point the introduction of the protective gas can be stopped.

[0097] Next, the temperature inside the vapor deposition apparatus can be raised to 300°C to 800°C and held at that temperature before proceeding to step S202. Exemplarily, the temperature inside the vapor deposition apparatus can be raised to 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, or other values ​​within the range of 300°C to 800°C. In some preferred embodiments, the temperature inside the vapor deposition apparatus can be raised to 400°C to 600°C.

[0098] A suitable temperature range is beneficial for controlling the reaction rate and the growth of Si grains. If the temperature is too low, the silicon-containing gas may not be able to decompose to generate silicon atoms, which may result in the inability to deposit silicon material or an insufficient amount of silicon material deposited. If the temperature is too high, the reaction rate may be too fast, leading to an excessively rapid growth rate of Si grains, resulting in large crystalline silicon particles. It may even prevent the silicon-containing gas from diffusing into the porous material, forming a hard shell on the surface of the porous material, which affects the cycle performance of the anode material.

[0099] In step S202, silicon-containing gas is introduced into the vapor deposition equipment in a pulse manner. Due to the instantaneous high energy input of the pulse discharge, the deposition process can be completed rapidly in a short time, which makes it easier to prepare anode materials with the same Si content in a shorter time, thereby increasing the deposition rate.

[0100] In some embodiments, the silicon-containing gas introduced in step S202 may include one or more of the following: silane, dichlorosilane, propane, butane, monochlorosilane, dichlorosilane, trichlorosilane, methyltrichlorosilane, dimethyldichlorosilane, tetrachlorosilane, etc. In other embodiments, the pulse pressure during the deposition process is controlled to be between -3 kPa and 7 kPa. For example, the pulse pressure may be -3 kPa, -2 kPa, -1 kPa, 0 kPa, 3 kPa, 3.5 kPa, 4 kPa, 4.5 kPa, 5 kPa, 5.5 kPa, 6 kPa, 6.5 kPa, 7 kPa, etc., or other values ​​within the range of -3 kPa to 7 kPa. When the pulse pressure is negative, it indicates that the deposition process is carried out under conditions below atmospheric pressure (i.e., vacuum).

[0101] According to the embodiments of this application, the pulse pressure is controlled within a low range, which allows for a shorter charging time. This prevents the Si atoms from silane decomposition at high temperatures from agglomerating into large molecules. Furthermore, the higher gas flow rate prevents crust formation on the surface of the porous material, ensuring timely replenishment of Si atoms deposited within the porous material. This improves the uniformity of Si atom distribution in the negative electrode material. In particular, during the later stages of deposition (i.e., the later densification stage), the adsorption capacity of the porous material decreases because many pores within the particles are already filled with silicon material, making surface crust formation more likely. However, by using the pulsed method and controlling the pulse pressure within a low range, Si atoms can continue to deposit into the pores of the porous material, resulting in more uniform silicon filling within the porous material and increasing the amount of silicon deposited.

[0102] If the pulse pressure is too low, it affects the deposition rate of silicon material. If the pulse pressure is too high and the gas filling time is too long, the silicon-containing gas undergoes a more complete cracking reaction, generating intermediate products that are large molecular clusters, hindering the transport of silicon-containing gas. As the densification process proceeds, the densification front of the porous material gradually moves to the outer surface, and a large amount of Si is cracked and deposited on the outer surface of the porous material, blocking the transport channels of silicon-containing gas, resulting in a further increase in the difference in Si atomic content between the inside and outside of the material particles.

[0103] In some other embodiments, the frequency of the controlled pulse bias voltage in step S202 is 200Hz to 1000Hz. For example, the frequency of the pulse bias voltage can be 200Hz, 300Hz, 400Hz, 500Hz, 600Hz, 700Hz, 800Hz, 900Hz, 1000Hz, or other values ​​within the range of 200Hz to 1000Hz.

[0104] The frequency of the pulse bias voltage refers to the number of times the pulse signal appears per unit time (per second) when the pulse power supply applies a bias voltage, and the unit is Hertz (Hz). In the preparation method of this application, the pulse bias voltage provides energy and driving force for the reaction and deposition of silicon-containing gas. The frequency of the pulse bias voltage determines the number of times the reaction and deposition processes occur per unit time. A higher pulse bias voltage frequency means more energy input and reaction opportunities per unit time, which will accelerate the reaction and deposition rate; a lower pulse bias voltage frequency results in a relatively slower reaction and deposition rate.

[0105] By controlling the frequency of the pulse bias voltage within the range of 200Hz to 1000Hz, the heat generated by the reaction can be fully diffused. Under conditions of higher overpotential and lower concentration polarization, the nucleation rate of Si grains is much greater than the growth rate of Si grains, thereby achieving a uniform Si distribution within the porous material and improving the deposition uniformity of silicon materials.

[0106] If the pulse bias frequency is too low, fewer pulses are released, resulting in slower reaction and deposition rates and a smaller amount of silicon material deposited. If the pulse bias frequency is too high, more pulses are released per unit time, and the pulse time interval is shortened, reducing heat dissipation efficiency and leading to heat accumulation. Under the action of adjacent pulses, Si tends to aggregate, accelerating the growth rate of Si grains and easily forming large Si grains, which is detrimental to the cycle performance of the anode material.

[0107] In some implementations, the duty cycle in step S202 can be controlled to be 0.15 to 0.85. For example, the duty cycle can be 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, or other values ​​within the range of 0.15 to 0.85.

[0108] Duty cycle refers to the ratio of the time a pulse signal is at a high level within one pulse cycle to the total pulse cycle time. In this embodiment, the duty cycle is controlled within the aforementioned range, making the total discharge and total energy storage more suitable. This increases the continuity of the transition of silicon-containing gas to the porous material, allowing the silicon-containing gas to transition more quickly to the surface and interior of the porous material. This improves the continuity and uniformity of silicon material deposition, resulting in a gradual increase in the amount of silicon material deposited.

[0109] If the duty cycle is too small, the single-pulse discharge energy and average current density are low, resulting in a low Si particle generation rate and a low silicon-containing gas diffusion rate. This does not provide sufficient time for the porous material to adsorb Si, leading to a low Si deposition rate and poor deposition uniformity. If the duty cycle is too large, the total energy released in a single pulse cycle will be too high, causing violent reactions in the silicon-containing gas, overheating within the vapor deposition equipment, a large heat-affected zone, and even the eruption of a strong electric arc, resulting in poor Si deposition uniformity.

[0110] Based on the above analysis, it can be seen that the embodiments of this application introduce silicon-containing gas into the vapor deposition equipment in a pulse manner, and control the pulse pressure during the deposition process to be -3kPa to 7kPa, the pulse bias frequency to be 200Hz to 1000Hz, and the duty cycle to be 0.15 to 0.85, thereby comprehensively controlling the deposition process and thus being able to prepare a negative electrode material with uniform silicon material distribution, so that the γ value of the negative electrode material meets the characteristic of ≤0.4.

[0111] It is understandable that introducing silicon-containing gas into a vapor deposition apparatus in a pulsed manner to carry out the deposition reaction can also be called pulsed chemical vapor deposition (PCVD). This method utilizes a pulsed power supply to generate high-energy particles during gas discharge. These high-energy particles react chemically with reactants in the gas phase to form a solid deposit. The "pulsed" manner refers to the instantaneous injection of silicon-containing gas to the required pressure via a pulsed power supply, allowing the silicon-containing gas to diffuse throughout the porous material, achieving deposition in a short time, followed by rapid exhaust of the waste gas. This cycle significantly reduces the concentration gradient generated during the diffusion of silicon-containing gas within the porous material, effectively avoiding the problem of uneven silicon deposition.

[0112] Further, in step S202, the total duration of silicon-containing gas introduction can be controlled to be between 60 min and 1200 min. Exemplarily, the total introduction time can be 60 min, 100 min, 200 min, 300 min, 400 min, 500 min, 600 min, 700 min, 800 min, 900 min, 1000 min, 1100 min, 1200 min, etc., or other values ​​within the range of 60 min to 1200 min. In some preferred embodiments, the total introduction time of silicon-containing gas is between 90 min and 480 min. In other preferred embodiments, the total introduction time of silicon-containing gas is between 120 min and 360 min.

[0113] In some embodiments, the flow rate of the silicon-containing gas can be controlled to be from 0.5 L / min to 50 L / min, for example, it can be 0.5 L / min, 1 L / min, 2 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, etc., or other values ​​within the range of 0.5 L / min to 50 L / min. In some preferred embodiments, the flow rate of the silicon-containing gas can be from 1 L / min to 20 L / min. In a further preferred embodiment, the flow rate of the silicon-containing gas can be from 2 L / min to 10 L / min.

[0114] In some embodiments, in step S202, a dilution gas may be introduced simultaneously with the silicon-containing gas. In other embodiments, the dilution gas may include hydrogen or the like. In still other embodiments, the flow rate of the dilution gas can be controlled to be 0.5 L / min to 50 L / min, for example, 0.5 L / min, 1 L / min, 2 L / min, 5 L / min, 10 L / min, 15 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, or other values ​​within the range of 0.5 L / min to 50 L / min. In some preferred embodiments, the flow rate of the dilution gas can be 2 L / min to 20 L / min. In a further preferred embodiment, the flow rate of the dilution gas can be 5 L / min to 10 L / min.

[0115] The deposition reaction rate can be controlled by introducing a dilution gas. By introducing hydrogen as a dilution gas, the rate at which silicon-containing gases decompose to generate Si atoms can be controlled. This avoids an excessively fast deposition reaction rate, thus preventing silicon material from depositing on the surface of porous materials and forming a hard shell, which would hinder further silicon deposition. In some embodiments, the negative electrode material obtained after the aforementioned deposition reaction can be carbon-coated. In other embodiments, the carbon coating treatment can include at least one of gas-phase coating, liquid-phase coating, and solid-phase coating. In still other embodiments, the carbon coating treatment can be gas-phase coating, and the carbon source in the carbon coating treatment can include one or more gaseous carbon sources such as methane, ethylene, and propane.

[0116] In some embodiments, the carbon coating treatment temperature is 500℃ to 650℃, the time is 1h to 6h, and the volume fraction of the carbon source gas is 6% to 60%. The carbon source gas can be diluted with an inert gas, including one or more of nitrogen, argon, and helium. Exemplarily, the carbon coating treatment temperature can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, etc., or other values ​​within the range of 500℃ to 650℃. The carbon coating treatment time can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, etc., or other values ​​within the range of 1h to 6h. The volume fraction of the carbon source gas can be 6%, 10%, 20%, 30%, 40%, 50%, 60%, or other values ​​within the range of 6% to 60%.

[0117] By carbon coating the anode material, one or more robust "shells" (i.e., carbon coating layers) can be added to the surface of the anode material to suppress the volume change that may occur during cycling. This can help improve the cycling performance of the anode material and also make the prepared anode material have better electronic conductivity and less overall gas production, thus obtaining anode materials with superior comprehensive performance.

[0118] Furthermore, in some embodiments, the preparation method 200 may further include, after the deposition reaction is completed, lowering the temperature inside the vapor deposition equipment to room temperature, removing the negative electrode material, and performing post-processing such as pulverization, sieving, and demagnetization. In some embodiments, pulverization may be performed using any one of an air jet mill, a ball mill, a turbine mill, etc. In other embodiments, sieving may be performed using any one of a vibrating screen, an air classifier, etc.

[0119] In yet another aspect, this application provides a secondary battery comprising the negative electrode material described in any one of the preceding first aspects of this application, or according to the foregoing combination. Figure 2 The described preparation method yields a negative electrode material. 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. The casing can be a packaging bag encapsulated with an encapsulation film (such as an aluminum-plastic film), for example, a pouch battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc. The secondary battery of this application embodiment also includes, for example... Figure 1 The electrode components shown, such as the positive electrode and the separator, will not be described in detail here.

[0120] Examples and comparative examples:

[0121] To better understand the performance of the negative electrode material and its preparation method according to the embodiments of this application, specific examples will be described below. Several comparative examples are also provided below to further illustrate the advantages of the negative electrode material according to the embodiments of this application.

[0122] Example 1:

[0123] Step 1) Load 2 kg of activated carbon into the vapor deposition furnace and evacuate to 10 °C. -2 Pa;

[0124] Step 2) Under the inert protective gas flow, start the furnace heating system to heat the vapor deposition furnace at a heating rate of 5℃ / min; the inert protective gas is argon with a flow rate of 10L / min; after the inert protective gas is introduced into the vapor deposition furnace, the oxygen content is lower than 50ppm; then stop the introduction of the inert protective gas.

[0125] Step 3) After heating to 500℃, maintain the temperature and introduce silane into the vapor deposition furnace for a total duration of 240 min at a flow rate of 5 L / min. Simultaneously, introduce dilution gas hydrogen at a flow rate of 10 L / min. Control the pulse pressure to 0 kPa to 3 kPa, the pulse bias frequency to 500 Hz, and the duty cycle to 0.5.

[0126] Step 4) Raise the temperature to 575℃ for 3.5 hours, with the volume fraction of the carbon source gas being 6% to 60%.

[0127] Step 5) After cooling the product obtained in Step 4) to room temperature, it is crushed, sieved and demagnetized to obtain the negative electrode material. The crushing is carried out by an air jet mill and the sieving is carried out by an air classifier.

[0128] Example 2: The only difference from Example 1 is that in step 3), the pulse pressure is -3kPa to 0kPa.

[0129] Example 3: The only difference from Example 1 is that in step 3), the pulse pressure is 3kPa to 7kPa.

[0130] Example 4: The only difference from Example 2 is that in step 3), the duty cycle is 0.15.

[0131] Example 5: The only difference from Example 2 is that in step 3), the duty cycle is 0.85.

[0132] Example 6: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 200Hz.

[0133] Example 7: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 1000Hz.

[0134] Example 8: The only difference from Example 1 is that step 4 is omitted.

[0135] Example 9: The only difference from Example 1 is that in step 3), the pulse pressure is -7kPa to -3kPa.

[0136] Comparative Example 1: The only difference from Example 1 is that in step 3), the pulse pressure is 7 kPa to 10 kPa.

[0137] Comparative Example 2: The only difference from Example 1 is that in step 3), the duty cycle is 0.1.

[0138] Comparative Example 3: The only difference from Example 1 is that in step 3), the duty cycle is 0.9.

[0139] Comparative Example 4: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 100Hz.

[0140] Comparative Example 5: The only difference from Example 1 is that in step 3), the frequency of the pulse bias voltage is 2000Hz.

[0141] Comparative Example 6: The only difference from Example 1 is that in step 3), the total time for introducing silane is 30 min.

[0142] Comparative Example 7: The only difference from Example 1 is that in step 3), the total time for introducing silane is 2000 min.

[0143] Comparative Example 8: The only difference from Example 1 is that, in step 3), the flow rate of silane is 0.2 L / min.

[0144] Comparative Example 9: The only difference from Example 1 is that, in step 3), the flow rate of silane is 100 L / min.

[0145] Performance testing methods:

[0146] This application also conducted the following performance tests on the anode materials prepared in the above embodiments and comparative examples:

[0147] (1) Test method for particle size of negative electrode material:

[0148] The particle size distribution range of the negative electrode material was tested using a Malvern laser particle size analyzer (Mastersizer 3000). The cumulative particle size distribution based on volume was determined by laser diffraction. The measurements were taken with reference to GB / T 19077.1-2008 "Particle size analysis by laser diffraction - Part 1: General rules" or the equipment manual, and Dv10, Dv50, and Dv90 were obtained.

[0149] (2) Method for testing specific surface area:

[0150] The specific surface area and pore size analyzer (TriStar 3000 & 3020, USA) was used to test the specific surface area of ​​powder samples using the gas adsorption method (nitrogen adsorption multi-point BET) under low-temperature controlled liquid nitrogen cooling. The specific procedure included: weighing a certain amount of sample and placing it into a dedicated specific surface area tube; purging the sample with nitrogen at 300℃ for a certain period of time in a degassing station; cooling to room temperature after degassing; weighing the actual mass of the sample; installing the dedicated tube containing the sample into the specific surface area and pore size analyzer; inputting the sample mass; and starting the specific surface area measurement. The sample density sampling range was 0.05 g / cm³. 3 ~0.30g / cm 3 Every 0.05g / cm 3 Take a data point.

[0151] (3) True density test method:

[0152] The measurement was performed according to GB / T 24533-2019, Appendix D, "Determination of True Density" or the equipment instruction manual. A true density meter (Bestde 3H-2000TD) was used. Helium was used as the gas.

[0153] (4) Test methods for pore volume and pore diameter:

[0154] Using a Micromeretics ASAP 246 pore size analyzer and the BET pore size distribution test method, the pore size distribution data of the material was obtained through DFT simulation analysis using the isothermal adsorption characteristic curve of nitrogen, and then the average pore size and pore volume of the material were obtained.

[0155] (5) Test method for powder conductivity:

[0156] The four-probe method was used to determine the volume resistivity of the sample. Using the MCP-PD51 powder conductivity meter from Mitsubishi Chemical (Japan), the conductivity of the powder at five pressure points (4, 8, 12, 16, and 20 kN) can be measured, and then the resistivity of the powder is automatically calculated by computer. The specific testing method includes: placing the test sample into a circular mold cavity. Four equally spaced probes, numbered 1, 2, 3, and 4, are fixed on a ceramic disc at the bottom center of the mold cavity. In the mold cavity filled with the sample, a cylindrical top post with a ceramic probe of the same diameter as the mold cavity is used to apply pressure to the sample, causing the four probe electrodes on the ceramic disc at the bottom of the sample in the mold cavity to come into close contact and be gradually pressed together. A current I passes between probes numbered 1 and 4, and a potential difference V is generated between probes numbered 2 and 3. By using the dynamic four-probe method to test the resistance of the circular block material under different pressures, the resistivity and conductivity of the powder sample under different pressures can be accurately calculated, and the relationship curve between pressure and conductivity can be obtained.

[0157] (6) Test method for compaction density:

[0158] The CARVER 4350.22 powder compaction density meter from McNaught (USA) was used. A sample of a specified mass was placed in a mold, a pressure of 1.0T was applied, and the pressure was maintained for 30 seconds. After the pressure was released, the thickness was measured, and the compaction density was calculated. Specifically, a certain mass of powder sample was placed in a metal sleeve, and the mass of the sample was measured as the ratio of the mass to the compacted volume after maintaining a certain pressure for a certain period of time.

[0159] (7) Test method for tap density:

[0160] The DAT-6-220 tap density meter from CANTA (USA) was used. A sample of a specified mass was placed in a graduated cylinder and vibrated a specified number of times (3000 times for routine testing). The volume of the graduated cylinder after vibration was read and the tap density was calculated. The specific operating steps are as follows: a certain mass of powder sample is placed in a graduated cylinder, and the instrument is used to vertically vibrate the sample at the set vibration frequency and number of times. The ratio of the mass to the volume of the sample after vibration is completed is the tap density of the sample.

[0161] (8) Gas production test method:

[0162] ① Prepare the slurry at room temperature according to a certain ratio: Carboxymethyl cellulose (CMC) is glued at a ratio of 1.4 wt%, dispersed evenly, and then 10 g of glue solution is mixed with 10 g of sample to make the slurry. ② Pack the slurry into an aluminum-plastic film bag and record the slurry mass; then seal it to form a sealed aluminum-plastic film bag. ③ Measure the volume of gas produced: Fix the sealed aluminum-plastic film bag at the bottom of the container, completely immerse it in water, and record the volume of the aluminum-plastic film bag. ④ After 24 hours, record the volume of the aluminum-plastic film bag again. ⑤ Calculate the gas production of the negative electrode material based on the change in the volume of the aluminum-plastic film, unit: mL / g / day;

[0163] (9) Method for testing the mass content of carbon:

[0164] A Bruker G4 ICARUS HF infrared carbon-sulfur analyzer from Germany was used. The sample was burned under high-temperature, oxygen-enriched conditions, where the carbon was oxidized to carbon dioxide. The generated gas entered the infrared detector along with the carrier gas. The mass content of carbon was calculated by quantitatively analyzing the changes in the carbon dioxide signal. The specific procedure was as follows: a certain amount of sample was weighed and placed in a ceramic crucible, flux was added, and the crucible was placed in a high-frequency furnace where high-purity oxygen was introduced for combustion to generate carbon dioxide. The carbon content in the gas was then measured using an infrared detector.

[0165] (10) Test method for the mass content of silicon:

[0166] A Nanyang Xinyu SA2-9-17TP box-type atmosphere furnace was used to ignite the sample in an oxygen atmosphere, causing silicon in the sample to react and become silicon dioxide, while carbon was burned and released as carbon dioxide. The mass content of silicon was calculated by weighing. The specific operating procedure was as follows: Weigh 1.0000g to 1.2000g of the sample into a corundum crucible, accurate to 0.1mg, with two parallel samples weighed for each sample. The muffle furnace heating program was set as follows: initial temperature 30℃, rising to 400℃ after 30 minutes and holding at 400℃ for 60 minutes (this step is to thoroughly remove moisture and low-boiling-point volatiles); then continuing for 60 minutes to rise to 900℃ and holding at 900℃ for 120 minutes (this step is to remove carbon and other volatile impurities); then continuing for 30 minutes to rise to 1100℃ and holding at 1100℃ for 480 minutes (this step is to complete the oxidation reaction from silicon to silicon dioxide); finally, the furnace was stopped, i.e., heating was turned off and cooling began.

[0167] (11) Methods for removing silicon material from negative electrode materials:

[0168] While stirring, a 20% HF acid solution was added dropwise to 10g of anode material. Yellow fumes (SiF4 and H2 gases) were generated and heat was released. After no more yellow fumes were generated in the solution, the supernatant acid solution was removed by centrifugation. Finally, 150ml of a 20% HF acid solution was added and stirred for 12h. The supernatant acid solution was then removed to dissolve the residue. The anode material was then washed with pure water until neutral and dried to obtain the anode material after removing the silicon material.

[0169] (12) Test method for Si atom content at different depths in anode materials:

[0170] X-ray photoelectron spectroscopy (XPS) of the anode material was performed using a Thermo Scientific K-Alpha instrument. The entire testing process was conducted in an argon-filled glove box. Each spectral acquisition required fine-spectrum analysis of C, O, and Si elements, with each argon ion sputtering depth being D. Taking D = 20 nm and equidistant etching as an example, the specific testing mode was as follows: no treatment was performed, and spectral acquisition was conducted to obtain the atomic percentage of Si on the surface; spectral acquisition was followed by etching at a depth of 20 nm, and this cycle was repeated 8 times. In the first cycle, the atomic percentage of Si at a depth of 20 nm was measured; in the second cycle, the atomic percentage of Si at a depth of 40 nm was measured; and so on, until the atomic percentage of Si at a depth of 160 nm was measured in the eighth cycle. This test was repeated for any 100 different regions at the same depth of the anode material, and the average value was taken to obtain the Si atomic content at each depth. Based on this, the required Si atomic contents at multiple depths could be selected, and the γ value could be calculated to determine the uniformity of Si atom distribution in the anode material.

[0171] (13) Electrochemical performance testing methods:

[0172] Button cell testing method: A negative electrode slurry was prepared by mixing negative electrode material, conductive carbon black, and polyacrylic acid (PAA) in a mass ratio of 70:15:15. This slurry was coated onto copper foil and dried to form a negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the coin cells were assembled in a glove box filled with Ar gas. The coin cells were charged and discharged at a current density of 0.1C within a charge-discharge range of 0.01V to 5V to obtain the initial reversible specific capacity (or initial discharge specific capacity) and initial coulombic efficiency (ICE) of the coin cells.

[0173] Cyclic expansion performance test method: A negative electrode slurry was prepared by mixing the test material with conductive carbon black Super-P, expanded graphite KS-6, carboxymethyl cellulose CMC, and styrene-butadiene rubber SBR in a mass ratio of 92:2:2:2:2. This slurry was then coated onto copper foil and dried to form a negative electrode sheet. The test material included a mixture of negative electrode material and graphite; the proportions of the negative electrode material and graphite in the mixture were determined by their initial reversible specific capacity and the required combined capacity. A coin cell was assembled using a lithium metal sheet as the counter electrode in a glove box filled with Ar gas. The coin cell was subjected to 50 repeated charge-discharge cycles at a current density of 1C within a charge-discharge range of 0.01V to 5V to obtain the capacity retention rate and electrode thickness expansion rate after 50 cycles.

[0174] To facilitate the description of the differences between the above embodiments and comparative examples, as well as the test results of each embodiment and comparative example, further explanation will be provided below in conjunction with Tables 1 to 5. Tables 1 to 5 show the test results of the negative electrode material samples prepared in each embodiment and comparative example, with Table 4 showing the test results after removing silicon material from the negative electrode material. In Table 2, taking XPS etching at multiple depths with an equidistant distance D = 20 nm as an example, A0 represents the Si atom content on the particle surface of the negative electrode material, A1 represents the Si atom content at a depth of 20 nm from the particle surface to the particle core, A2 represents the Si atom content at a depth of 40 nm from the particle surface to the particle core, A3 represents the Si atom content at a depth of 60 nm, A4 represents the Si atom content at a depth of 80 nm, A5 represents the Si atom content at a depth of 100 nm, A6 represents the Si atom content at a depth of 120 nm, A7 represents the Si atom content at a depth of 140 nm, and A8 represents the Si atom content at a depth of 160 nm. γ is calculated based on these nine Si atom contents.

[0175] Table 1:

[0176]

[0177] Table 2:

[0178] A0 A1 A2 A3 A4 A5 A6 A7 A8 γ Example 1 17 11 16.3 16.8 22.7 23.6 23.9 23.0 23.5 0.3 Example 2 10 15.9 12.3 16.4 18 17.5 18.5 18.0 18.3 0.295 Example 3 15 15 16.7 17 23.3 22.9 23.8 23.0 23.4 0.315 Example 4 16 15.7 15.4 16.2 21.1 23.3 23.5 24.0 23.7 0.245 Example 5 14 13.1 12.7 16.4 22.6 22.1 23.5 23.0 23.3 0.31 Example 6 13.8 8.4 14.2 16.5 24.1 24.6 24.9 24.0 24.5 0.38 Example 7 12.0 14.0 13.2 16.9 22.8 22.5 23.1 23.0 23.1 0.31 Example 8 5.1 10.9 16.6 16.5 22.1 22.4 23.0 22.4 22.8 0.28 Example 9 17.2 17.3 17 16.6 17.9 17.8 17.4 17.0 17.2 0.065 Comparative Example 1 14.7 11.5 10.4 22.6 19.9 18.3 23.1 23.0 23.1 0.61 Comparative Example 2 4.2 17.9 6.6 16.1 21.5 16.0 19.7 19.0 19.4 0.685 Comparative Example 3 8.4 16.9 12.9 10.0 15.9 12.3 16.4 16.0 16.2 0.425 Comparative Example 4 3.9 12.2 12.4 12.9 13.4 12.8 13.5 13.0 13.3 0.415 Comparative Example 5 4.7 13.8 20.3 16.7 20.8 17 21.5 21.0 21.3 0.455 Comparative Example 6 5 4.3 3.7 14.5 15.5 16 15.1 15.0 15.1 0.54 Comparative Example 7 20 20.5 17.7 28.3 20.3 21.8 20 21 20.5 0.53 Comparative Example 8 4.4 5.2 6.3 16.1 15.8 16.6 15.5 15.0 15.3 0.49 Comparative Example 9 27.5 28.8 28.3 20.2 18.1 20.4 20.0 19 19.5 0.405

[0179] Table 3:

[0180]

[0181] Table 4: Test results of anode material after removing silicon material

[0182]

[0183]

[0184] Table 5:

[0185]

[0186] The data in Tables 1 to 5 above show that:

[0187] (1) As can be seen from Tables 1 to 5, during the preparation of the negative electrode materials in Examples 1 to 8, different pulse pressures, duty cycles, and pulse bias frequencies were controlled. The negative electrode materials prepared all met the condition γ≤0.4, indicating that the Si element in the prepared negative electrode materials was relatively uniformly distributed. Furthermore, the first discharge specific capacity, first coulombic efficiency, electrode thickness expansion rate after 50 cycles, and capacity retention rate all showed excellent performance.

[0188] (2) As can be seen from Tables 1 to 5, the negative electrode material of Example 9 satisfies γ≤0.4, indicating that the distribution of Si elements in the negative electrode material is relatively uniform, which reduces the electrode thickness expansion rate after 50 cycles, improves the capacity retention rate, and enhances the cycling performance of the negative electrode material. However, compared with Example 1, the total pore volume of Example 9 is larger, and the volume ratio of micropores reaches 20%, indicating that the amount of silicon material deposited in the negative electrode material of Example 9 is smaller, thus affecting its initial discharge specific capacity and initial coulombic efficiency.

[0189] (3) As can be seen from Tables 1 to 5, the negative electrode material was prepared using a pulse pressure greater than 7 kPa in Comparative Example 1. Compared with Example 1, the negative electrode material of Comparative Example 1 has a higher gas production rate and γ > 0.4, indicating that the distribution of Si atoms in the negative electrode material is not uniform, which affects the capacity retention rate of the negative electrode material in long cycle and increases the electrode thickness expansion rate, which is not conducive to the cycle life and safety performance of the battery.

[0190] (4) As can be seen from Tables 1 to 5, in the preparation of the negative electrode material in Comparative Example 2, the duty cycle was controlled at 0.1. Compared with Example 1, the γ of the negative electrode material in Comparative Example 2 is greater than 0.4, indicating that the Si atom content distribution in the negative electrode material is not uniform, thus affecting the cycle performance of the negative electrode material. In addition, compared with Example 1, the total pore volume of the negative electrode material in Comparative Example 2 is larger, and the volume ratio of micropores is greater than 10%, while the volume ratio of mesopores is less than 80%. Given that the negative electrode materials of Comparative Example 2 and Example 1 have similar pore size and pore volume after removing silicon material, it indicates that the amount of silicon material deposited in the negative electrode material of Comparative Example 2 is less, thus affecting its initial discharge specific capacity and initial coulombic efficiency.

[0191] (5) As can be seen from Tables 1 to 5, in Comparative Example 3, the duty cycle was controlled at 0.9 during the preparation of the negative electrode material. The higher duty cycle resulted in a higher mass content of Si in the prepared negative electrode material, thereby improving its initial discharge specific capacity and initial coulombic efficiency. However, the negative electrode material of Comparative Example 3 had γ > 0.4 and gas production > 1 mL / g / day, indicating that the excessively large duty cycle resulted in poor uniformity of Si atom distribution in the negative electrode material, which in turn affected the capacity retention rate of the negative electrode material after 50 cycles, increased the electrode thickness expansion rate, and was not conducive to improving the cycle performance and safety performance of the negative electrode material.

[0192] (6) As can be seen from Tables 1 to 5, the γ of the negative electrode material in Comparative Example 4 is greater than 0.4. In the preparation of the negative electrode material in Comparative Example 4, a pulse bias frequency of 100Hz was used. Compared with Example 1, the initial discharge specific capacity and initial coulombic efficiency of the negative electrode material in Comparative Example 4 are both lower. Therefore, compared with Comparative Example 4, the overall performance of the negative electrode material in Example 1 is better.

[0193] (7) As can be seen from Tables 1 to 5, Comparative Example 5 used a pulse bias frequency of 2000 Hz in the preparation of the negative electrode material. Compared with Example 1, the higher pulse bias frequency resulted in a higher Si content in the prepared negative electrode material, thereby improving its initial discharge specific capacity and initial coulombic efficiency. However, the negative electrode material of Comparative Example 5 had γ > 0.4 and gas production > 1 mL / g / day, indicating that the excessively high pulse bias frequency caused the uniformity of Si atom distribution in the negative electrode material to deteriorate, which in turn affected the capacity retention rate of the negative electrode material after 50 cycles, increased the electrode thickness expansion rate, and reduced the cycle performance and safety performance of the negative electrode material.

[0194] (8) As can be seen from Tables 1 to 5, the γ of the negative electrode material in Comparative Example 6 is greater than 0.4. Since the total time for introducing silane during the preparation of the negative electrode material in Comparative Example 6 was only 30 minutes, the excessively short total time for introducing silicon-containing gas affected the total amount of silicon-containing gas introduced, resulting in a low mass content of Si in the negative electrode material and a large total pore volume, with micropores accounting for as much as 49% of the volume. Given that the negative electrode materials of Comparative Example 6 and Example 1 have similar pore sizes and volumes after removing silicon, it indicates that compared to Example 1, the amount of silicon material deposited in the negative electrode material of Comparative Example 6 is too small, leading to a significant decrease in its initial discharge specific capacity and initial coulombic efficiency. Therefore, compared to Comparative Example 6, the negative electrode material of this application has superior overall performance.

[0195] (9) As can be seen from Tables 1 to 5, in the preparation of the negative electrode material in Comparative Example 7, the total time for introducing silane was 2000 min. Compared with Example 1, the higher total time for introducing silicon-containing gas resulted in a higher mass content of Si in the prepared negative electrode material. Although this significantly improved its initial discharge specific capacity and initial coulombic efficiency, the negative electrode material of Comparative Example 7 had a γ > 0.4, indicating poor uniformity of Si atom deposition. This led to a gas production rate of > 1 mL / g / day for the negative electrode material of Comparative Example 7, resulting in poor capacity retention and electrode thickness expansion rate after 50 cycles, which affected the cycle performance and safety performance of the negative electrode material. Therefore, compared with Comparative Example 7, the negative electrode material of Example 1 has better overall performance.

[0196] (10) As can be seen from Tables 1 to 5, the γ of the negative electrode material in Comparative Example 8 is greater than 0.4. In the preparation of the negative electrode material in Comparative Example 8, the flow rate of silane was only 0.2 L / min. The excessively low flow rate of silicon-containing gas affected the total amount of silicon-containing gas introduced, resulting in a low mass content of Si in the negative electrode material and a large total pore volume, with the micropore volume accounting for as much as 40%. Given that the negative electrode materials of Comparative Example 8 and Example 1 have similar pore size and pore volume after removing silicon material, it indicates that compared to Example 1, the amount of silicon material deposited in the negative electrode material of Comparative Example 8 is too small, resulting in a significant decrease in its initial discharge specific capacity and initial coulombic efficiency. Therefore, compared to Comparative Example 8, the negative electrode material of this application has superior overall performance.

[0197] (11) As can be seen from Tables 1 to 5, in the preparation of the negative electrode material in Comparative Example 9, the flow rate of silane was 100 L / min. The high flow rate of silicon-containing gas resulted in a high mass content of Si in the prepared negative electrode material. Although this significantly improved its initial discharge specific capacity and initial coulombic efficiency, the Si atom distribution in the negative electrode material of Comparative Example 9 was >0.4, indicating poor uniformity of Si atom distribution. Consequently, the gas production of the negative electrode material of Comparative Example 9 was >1 mL / g / day, and the capacity retention rate and electrode thickness expansion rate after 50 cycles were both poor, affecting the cycle performance and safety performance of the negative electrode material. Therefore, compared with Comparative Example 9, the negative electrode material of Example 1 has better overall performance.

[0198] In summary, this application provides a negative electrode material in which XPS etching is performed from the particle surface to the particle core at multiple depths to obtain Si atom content at multiple depths. The Si atom content at the particle surface and the Si atom content at the multiple depths satisfy the following: Furthermore, γ ≤ 0.4 indicates a uniform distribution of Si atoms in the negative electrode material. This results in a more dispersed stress distribution across the particles during charging and discharging, preventing stress concentration points and leading to superior cycle retention and lower expansion rate. On the other hand, the uniform distribution of Si atoms in the negative electrode material also reduces the likelihood of a sharp peak (0.45V–0.5V) on the dQ / dV curve due to the free growth of Si particles during charging and discharging. The presence of this peak corresponds to the presence of Li... 15 The Si4 phase is crystalline and involves an additional phase transformation during lithium insertion / extraction. Compared to other amorphous lithium-silicon alloys, this Li4 phase... 15 The insertion and extraction process of the Si4 phase is more difficult, which leads to the deterioration of its electrochemical performance. The negative electrode material provided in this application can effectively avoid this problem.

[0199] While numerous embodiments of this application 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 arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application 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 porous material and an active substance, wherein the active substance is at least partially distributed within the pores of the porous material, and the active substance includes a silicon material. XPS etching is performed from the surface of the negative electrode material particles to multiple depths towards the particle core to obtain the Si atom content at the multiple depths. The Si atom content at the particle surface and the Si atom content at the multiple depths satisfy the following: γ≤0.4; Wherein, γ represents the uniformity parameter of Si atom distribution in the negative electrode material, and A i A represents the Si atom content at the i-th depth out of n depths from the particle surface to the particle core of the negative electrode material. i-1 A0 represents the Si atom content at the (i-1)th depth out of n depths from the particle surface to the particle core of the negative electrode material, D represents the distance between the i-th depth and the (i-1)th depth, and n≥2.

2. The negative electrode material according to claim 1, characterized in that, From the particle surface to the particle core of the negative electrode material, the Si atom content at each depth is 17% to 25%.

3. The negative electrode material according to claim 1, characterized in that, The Si atom content on the surface of the particles is 5% to 17%; and From the particle surface to the particle core of the negative electrode material, the Si atom content at each depth is 5% to 17%.

4. The negative electrode material according to claim 2 or 3, characterized in that, The average Si atom content from the particle surface of the negative electrode material to the third depth is less than the average Si atom content from the fourth depth to the eighth depth.

5. The negative electrode material according to claim 1, characterized in that, The negative electrode material also satisfies at least one of the following characteristics: (1) The volume ratio of the micropore volume to the total pore volume of the negative electrode material is ≤10%; (2) The volume of mesopores in the negative electrode material accounts for ≥80% of the total pore volume; (3) The volume ratio of macropores in the negative electrode material to the total pore volume is ≤20%; (4) The total pore volume of the negative electrode material is 0.001 cm³. 3 / g~0.1cm 3 / g; (5) The average pore size of the negative electrode material is 0.45 nm to 50 nm; (6) The specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~10m 2 / g.

6. The negative electrode material according to claim 1, characterized in that, After the silicon material is removed from the negative electrode material, it satisfies at least one of the following characteristics: (1) The total pore volume is 0.2 cm³. 3 / g~1.5cm 3 / g; (2) The volume percentage of micropores in all pores is ≥15%; (3) The volume fraction of mesopores in all pores is ≤85%; (4) The volume percentage of macropores in all pores is ≤2%; (5) The volume percentage of pores smaller than 5 nm in all pores is ≥90%; (6) Specific surface area is 200m² 2 / g~3000m 2 / g; (7) The average pore size is 1.0 nm to 20 nm; (8) True density is 1.6 g / cm³ 3 ~2.4g / cm 3 .

7. The negative electrode material according to claim 1, characterized in that, The negative electrode material also satisfies at least one of the following characteristics: (1) The particle size distribution of the negative electrode material satisfies: 0.9≤(Dv90-Dv10) / Dv50≤5; (2) The volume median particle size Dv50 of the negative electrode material is 0.5 μm to 40 μm; (3) The volume median particle size Dv50 of the negative electrode material is 5μm to 20μm.

8. The negative electrode material according to claim 1, characterized in that, The negative electrode material also satisfies at least one of the following characteristics: (1) The compaction density of the negative electrode material is 0.8 g / cm³. 3 ~1.3g / cm 3 ; (2) The tap density of the negative electrode material is 0.5 g / cm³. 3 ~1.5g / cm 3 ; (3) The powder conductivity of the negative electrode material under a pressure of 20 kN is 0.1 S / cm to 2 S / cm; (4) The gas production of the negative electrode material is ≤1 mL / g / day.

9. The negative electrode material according to claim 1, characterized in that, The negative electrode material also satisfies at least one of the following characteristics: (1) The porous material includes at least one of activated carbon, capacitor carbon, carbon molecular sieve, graphene, zeolite, porous graphite, porous Al2O3, porous ZrO2, and porous TiO2; (2) The negative electrode material further includes a core and a carbon coating layer covering at least a portion of the surface of the core, wherein the core includes a porous material and an active substance; (3) Based on the mass of the negative electrode material, the mass content of silicon in the negative electrode material is 20% to 60%; (4) Based on the mass of the negative electrode material, the mass content of carbon element in the negative electrode material is 35% to 80%.

10. A secondary battery, characterized in that, The secondary battery includes the negative electrode material as described in any one of claims 1-9.

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